Several lines of evidence strongly indicate that hepatic stellate cells (HSCs), which reside in the perisinusoidal space of Disse, should be considered as an important cell type that participates in hepatic ischemia/reperfusion (I/R) injury, inflammation and immunity. HSCs are the contractile cells of the sinusoids, and produce the most potent hepatic vasoconstrictor endothelin-1 (ET-1), a major cause of I/R injury, in response to various stimuli including reactive oxygen species and gut-derived bacterial endotoxin (lipopolysaccharide, LPS). ET-1 acts on HSCs in an autocrine manner or on the extrasinusoidal smooth muscle cells in a paracrine manner to elicit such an effect. Further, LPS-conditioned HSC medium increases nuclear expression of IRF-1, an important mediator of I/R injury, in hepatocytes. Evidence also suggests that ET-1 can modulate maturation of DCs differentially upon binding to ETA or ETB receptor subtypes. HSCs are the principal storage site for retinoids, which are released during liver injury. The retinoid, retinoic acid, and TGF-P also produced by HSCs (and other cells, e.g. Kupffer cells), induce differentiation of CD4+ T cells into immunosuppressive FoxP3+ Treg cells. HSCs express and release FasL, which causes T cell apoptosis, produce several cytokines (e.g., TGF-(3, TNF-a, IL-6, IL-8, IL-10, IL-15), chemokines (e.g., MCP-1, MIP, RANTES) and T cell chemoattractants (CXCL9, CXCL10, CXCL11), and express adhesion molecules (ICAM-1,VCAM-1), antigen-presenting molecules (MHC-I and -II) and co-stimulatory (CD80, CD86, CD40) and inhibitory (PD-1) molecules. The concentration of LPS is increased in liver diseases and after liver transplantation until graft function is restored. LPS stimulates production of nitric oxide (NO), a potent vasodilator and immunomodulator, and also Increases the expression of FasL, CXCL9, CXCL10, CXCL11, TNF-a, IL-6 etc. in HSCs. Based on these observations, we hypothesize that the participation of HSCs in I/R, inflammatory and immunological processes is critically important in acceptance or rejection of the transplanted liver. Our Aims are- Aim 1: To investigate the role of hepatic stellate cells in liver ischemia/reperfusion injury. Aim 2: To investigate mechanisms underlying the regulation of dendritic cells and T lymphocyte responses by hepatic stellate cells. Aim 3: To investigate the role of hepatic stellate cells in the regulation of liver allograft outcome. The outcome of this proposal will reveal as yet unknown mechanisms by which HSCs regulate liver transplant outcome, which could be critical in the appropriate therapeutic developments. RELEVANCE (See instructions): Despite intense investigation over several years of liver transplant immunoregulation, many questions regarding the unfavorable outcome in a significant number of cases are unanswered. Due to acute shortage of donor organs and increasing costs and complications of liver transplantation, precise knowledge of these undefined mechanisms is critically important. Project 3 will address these questions with focus on a versatile cell type "stellate cells" with inflammatory, and growth and immunoregulatory properties. The knowledge gained, therefore, will be important in developing interventions for improved transplant outcome.